I would get a beware of the dog sign up that way its clearly marked you have a dog & in my opinion they would have to be pretty stuipd to shin a gate knowing a dogs very possibly on the other side of it.
I honestly dont think they will do anything like try & gain access , they may pay your property a a visit at some point , but if you get in first & offer some small weekly payment & make the lad see he has to take responsibility for his actions hopefully it will sort its self out , i know our sons are enough to make you fart blood & i dispare of mine but you dont want i